The present invention relates to an interconnection used in semiconductor devices, etc., more specifically to an interconnection which is suitably applicable to metal interconnections, semiconductor devices, methods for forming the metal interconnection and methods for fabricating the semiconductor devices which use Cu (copper) for lower resistivity.
As semiconductor integrated circuits have been recently higher integrated, elements formed on the semiconductor substrates and interconnections connecting the elements have been increasingly micronized. Accordingly, characteristics and reliability required of the interconnections have become stricter. More reliable interconnection materials having lower resistivity, electro migration resistance and stress migration resistance, etc. are needed.
In such background, Cu, which is superior to Al (aluminum) in resistivity and electro migration resistance, is noted as an interconnection material in place of Al, which has been conventionally widely used as an interconnection material, and has been increasingly practically used. In forming such copper interconnection on the semiconductor substrate, a fabrication process so-called damascene method is used to bury copper interconnection in the insulation film.
With reference to FIGS. 24A-24D, the method for fabricating a copper interconnection by damascene method will be explained. FIGS. 24A-24D are diagrammatic sectional views showing a method for fabricating a copper interconnection by damascene method on an inter-layer insulation film 101 formed above a semiconductor substrate in the sequence of the forming steps.
First, as shown in FIG. 24A, an interconnection groove 102 is formed in the inter-layer insulation film 101 formed on the semiconductor substrate (not shown), by photolithography and dry etching following the photolithography.
Then, as shown in FIG. 24B, a refractory metal film 103 is formed, covering the inter-layer insulation film 101 and the inside wall of the interconnection groove 102. The refractory metal film 103 is a barrier film which prevents Cu as the interconnection material from reacting with the inter-layer insulation film 101 of silicon oxide film, etc. and diffusing so as to suppress deterioration of device characteristics. Then, a Cu film 104 as a seed layer is formed by CVD method or others, covering the refractory metal film 103 so as to efficiently form the Cu film 105 to be formed by plating.
Then, as shown in FIG. 24C, a Cu film 105 is formed by sputtering method, so as to fill the interconnection groove 102. Thus, the interconnection groove 102 is filled with the Cu film 105 with the Cu film 105 formed thick in the region other than the interconnection groove 102.
Next, as shown in FIG. 24D, the Cu films 104, 105, and the refractory metal film 103 in the region other than the interconnection groove 102 are polished back by CMP (Chemical Mechanical Polishing) method. Thus, the interconnection film of the refractory metal film 103, the Cu films 104, 105 buried in the interconnection groove 102 is completed.
In thus using Cu as an interconnection material, because Cu produces no halogenide of high vapor pressure, dry etching cannot be used in the patterning. The interconnection must be formed by damascene method including the polishing step by CMP method.
However, the CMP method performed for removing the Cu films 104, 105 on the inter-layer insulation film 101 is a mechanical polishing method, and the Cu films 104, 105 are often peeled from the interconnection groove 102 by the mechanical stress.
Especially, the refractory metal film 103 is formed of TaN (Tantalum Nitride) or others, which has low reactivity with the Cu films 104, 105 so that the refractory metal film 103 can function as a barrier film. The refractory metal film 103 can prevent diffusion of the Cu into the inter-layer insulation film while cannot ensure sufficient adhesion to the Cu film 104. Accordingly, when the mechanical polishing is performed by CMP method, a stress is exerted to the interface between the Cu films 104, 105 and the refractor metal film 103 by a force applied to the Cu films 104, 105, and often the Cu films 104, 105 peel from the refractory metal film 103. When the adhesion between the refractory metal film 103 and the Cu film 104 is insufficient, the resistance to the stress migration cannot be sufficiently ensured.
When large current flows in the Cu films 104, 105, migration of atoms more tends to occur near the interface between the Cu film 104 and the refractory metal film 103 rather than inside of the interconnection film. However, because of poor adhesion between the refractory metal film 103 and the Cu film 104, there is a limit to the improvement of the electro migration resistance near the interface.
Notwithstanding the good advantage that the interconnection material using Cu can decrease resistivity and can improve electro migration resistance, it is essential to form the barrier layer, and sufficient adhesion cannot be ensured near the interface between the Cu film and the barrier layer of low reactivity with Cu. Accordingly, when the mechanical polishing is preformed by CMP method, the Cu films 104, 105 often peel off. The adhesion with respect to the refractory metal film 103 cannot be increased, and accordingly there is a limit to further improvement of the electro migration resistance and the stress migration resistance.